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A New Design For The Drake L4B
Written by: Ronald Baker / WB4HFN
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The Drake L4B
Amplifier was designed and built in the middle 1960's as a
two piece unit. This included the (L4B)
amplifier section and the (L4PS) high voltage power supply.
The amplifier was a very rugged amplifier and designed as a
two final tube amplifier using the 3-500 or similar tube.
Over the last 40 plus years the amplifier section has
survived well but the power supply is a different story.
The power supply by design produced over 2500 volts at
almost 1 AMP. Over time component
failures in many cases has deemed the power supply as being non-repairable.
Typical problems include dried out filter capacitors, load
resistors opening and high voltage arcing. In
most cases it is the lack of replacement parts or a bad
transformer as reasons for being non-repairable.
Today you can find a surplus of the L4B amplifiers
without the mating high voltage power supply.
The theme of this article presents one possibility in giving
the old girl a new life.
Shown in the
pictures below is the original Drake L4-B amplifier and the mating
L4PS high voltage power supply which Drake Manufacturing
sold between 1965 to around 1979.
The earlier version of the L4B the front panel had the
silver edging around the outside edge of the front panel all
around, this matched with the Drake B-Line series.
The later version of the L4B the front panel was painted
edge to edge to match with the newer Drake C-Line.
Table of Contents
The L4B Amplifier Chassis Redesign
The Input Circuit Redesign
The New High Voltage Circuit
Amplifier Metering And
The New Low Voltage Power
The Completed Redesigned
Drake L4B Amplifier
Related Article Links
L4/L4B Blower Fan Repair/Upgrade
High Speed Switching (QSK) For the Drake L4B Amplifier
Power Switch Refurbishing Project
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